Combined wulff process and coking process

ABSTRACT

UNSATURATED HYDROCARBONS ARE PREARED BY PYROLYSIS OF HYDROCARBONS IN A REGENERATIVE TYPE FURNACE, AND EFFLUENT GASES CONTAINING UNSATURATED HYDROCARBONS FFROM THE REGENERATIVE TYPE FURNACE ARE RAPIDLY QUENCHED WITH AN OIL QUENCH SYSTEM AND RECCLED TO A COKER WHICH CAN PROVIDE A PORTION OF THE FEEDSTOCK FOR THE FURNACE, A QUENCH OIL FOR THE QUENCHER, AND COKE AS A BY-PRODUCT.

March 12, 1974 B, STARZENSKl ETAL COMBINED WULFF PROCESS AND COKING PROCESS Filed Jan. 4, 1968 7 r0 ETHYLE/VE A/VD ACETYLE/VE PURIFICATION QUENCH r\ TOWER STEAM HYDROCARBO/V 5 WULFF I FURNACE S 8 r 3 COKER NAPHTHA l r M (JOKER FRACTIONATQR COKE/7 64$ OIL 9 lcoxs BOTTDMS FROM CRUDE TOWER -l/VVE/VTO/PS BRUCE R. STARZENSKI ROBERT H. REITSEMA ATTORNL'Y United States Patent US. Cl. 260-683 R Claims ABSTRACT OF THE DISCLOSURE Unsaturated hydrocarbons are prepared by pyrolysis of hydrocarbons in a regenerative type furnace, and efiluent gases containing unsaturated hydrocarbons from the regenerative type furnace are rapidly quenched with an oil quench system and recycled to a coker which can provide a portion of the feedstock for the furnace, a quench oil for the quencher, and coke as a by-product.

CROSS REFERENCES TO RELATED APPLICATIONS US. patent application Ser. No. 694,432 filed Dec. 29, 1967, now Pat. No. 3,629,353 and assigned to the assignee of the present invention, relates to the general field of the present invention.

BACKGROUND OF THE INVENTION Processes for thermally cracking hydrocarbons into acetylene, ethylene, and other unsaturated gases have been described at length in the literature. (See, for example, the Wulff Process described in US. Pats. 1,996,- 185; 2,037,056; 2,236,534; 2,236,535; 2,236,555; 2,319,- 679; 2,518,688; 2,526,696; and 2,908,625.) The pyrolysis of methane, ethane, propane, butane and natural gas to form acetylene and ethylene have particularly been studied. (See, for example, Tropsch and Engloif, Industrial and Engineering Chemistry, 27, p. 1063 (1935) and US. Pat. No. 1,983,992.) -As illustrated by 'FIG. 1 of US. 2,236,534, such processes typically consist of a furnace in which the thermal cracking of hydrocarbons is accomplished generally at temperatures above about 1500 F., through carefully controlled contact periods of generally less than about ten seconds. A rapid cooling of the eflluent from the furnace is usually essential to obtaining the desired ethylene and acetylene products. By control of the process conditions, the ratio of acetylene to ethylene can be controlled generally within a substantial range.

U.S. 2,908,625, issued to Mekler et a1., teaches the use of a coker to produce coker naphtha as feedstock for the regenerative furnace, in this case, a Wulff furnace. Current markets for petroleum products have made it economically expedient to utilize the Wulff process with much higher boiling feedstocks, such as those used in the Mekler et al. patent, than the gaseous aliphatic hydrocarbon feedstocks heretofore commonly employed. However, these feedstocks, primarily heavy naphthas boiling in the range of approximately 200-400 F., form substantially greater amounts of materials, including emulsions, which, while originally soft and tacky, solidify with time into relatively hard materials which are difficult to remove from the interior of downstream equipment.

SUMMARY OF THE INVENTION This invention relates principally to the production of unsaturated hydrocarbons, by a process utilizing basically a Wulif furnace, a coker, and a quench system.

In general a hydrocarbon diluted with steam is fed into the regenerative furnace, where it is cracked, partially cooled, to produce an eflluent stream containing unsatu- 3,796,768 Patented Mar. 12, 1974 rated hydrocarbons, which are then fed to a quenching system. This quencher utilizes oil, preferably from the coker, to rapidly reduce the temperature of the eflluent gases, and to simultaneously remove undesirable carbon particles, heavy hydrocarbon tars and readily polymerizable oils from the eflluent to minimize downstream deposits. After this is accomplished, a water quench may be used to further cool the efiluent gases and also to condense and remove water vapor (injected originally as the steam diluent) present in the effluent. The quench mediatar mixture is then removed from the quencher and recirculated to the coker. This mixture, along with other hydrocarbons present in the coker, is coked to produce a coker naphtha, a coker gas oil, and a by-product of coke, completing the quenching system cycle. The quenched gases are then separated and purified.

The present process is a substantial improvement over processes known to the art. First of all, the use of the oil quench essentially overcomes the problem of emulsion breaking encountered in traditional processes by avoiding the formation of oil-Water emulsions from the use of a water quench.

In preferred embodiments the invention supplies feed to the regenerative furnace, quench oil to the quencher, and means for recirculating the quench oil efiluent internally. In particular, the quench oil is obtained from the coker whereas in traditional processes of the art, water for the water quench had to be supplied externally. Furthermore, the quench oil-tar mixture effiuent is disposed of conveniently by recycling to the coker. The old problem of disposing of the quench oil-tar mixture effluent is thus avoided. The coker serves as a depository for the quench oil-tar mixture. It can also serve the additional purposes of producing coker naphtha feedstock for the Wullf furnace (as a portion of the hydrocarbon feed in the preferred embodiment of this invention) and, of course, produces coke.

Use of the coker as the source of the feed stock for the Wulif furnace has the advantage of allowing the system to tolerate heavy hydrocarbon feeds, yet lighter boiling fractions such as ethane, propane, or butane or other normally employed hydrocarbon feeds can be utilized in this system. Use of the tars as feed stock for the coker may enhance the quality of the coke produced.

A further advantage of the oil quench of this invention is that the need for a separate tar-separating unit is reduced since at least part of this separating capacity is built into the oil quench system.

The products, principally acetylene and ethylene, have uses not only as chemical intermediates in other chemical processes, but also acetylene, for instance, is excellent as a welding grade fuel. The uses of coke, e.g. electrodes, etc., are well known as are other advantages and uses of the principal products of this invention.

DESCRIPTION OF THE DRAWING The drawing is a schematic drawing of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Useful hydrocarbon starting materials for this invention include light aliphatic gaseous hydrocarbons such as ethane, propane, butane, or mixtures thereof, and liquid hydrocarbons, preferably coker naphthas boiling in the range of from to 400 F., and more preferably straight-run naphthas boiling in the range of 100 to 400 F. The most preferred hydrocarbon feed contains the overhead vapors from the coker mixed with straightrun naphthas. Super heated steam is mixed with the hydrocarbon feed, preferably in the ratio of from 1 to 10 (more preferably 3 to 8) moles of steam per mole of 3 hydrocarbon. The coker may be of the fluid type, but preferably is of the delayed type, the distinctions of which are well known to those skilled in the art.

The combined hydrocarbon and steam feed 1 enters the regenerative furnace 2 which may be, and is preferably of the Wulff furnace type, described in the above cited patents. The hydrocarbons are cracked at approximately 15002500 F. within the furnace and leave at approximately 350-600 F. The residence time is preferably less than ten seconds and more preferably less than about 0.2 second. The entire make and heat cycle of the Wulff furnace is similar to that described in Wulff Process Acetylene, Modern Chemical Processes, vol. 3, p. 2596, December 1953 in FIG. 4. Regenerative furnace processes in general are described in Acetylene, Encyclopedia of Chemical Technology, vol. I, pp. 184 through 186, and are also described in Acetylene, Miller, pp. 384 through 386.

A typical cracked gas analysis of the Wulif furnace efiiuent can be found on page 265 of Wulfl? Process Acetylene, Modern Chemical Processes, in Table IV. Wulif furnace effluents from other carbon feeds, such as the preferred straight-run coker naphtha feed mixture of the instant process, will generally not differ markedly from that described in said Table IV. The Wulif furnace efiiuent is now sent to the oil quencher 4 which is preferably two-staged and designed to have a low pressure drop. A number of standard type trays are used within each stage. In the bottom stage of the tower, two to three trays or shower heads are employed. The hot gases pass upward through the quench oil falling down the tower. The temperature of operation is preferably from about 300 to about 600 F. and more perferably 400 F. The purpose of this section is to remove carbon and the heaviest tars. Gas, now at about 300 to 500 F., passes into the upper oil quench stage were it is contacted by additional quench oil. Either the same boiling range oil can be used or a slightly lower one. Here the gas is cooled to a temperature which is approximately 10 F. greater than the condensation temperature for the steam in the gas. This temperature will vary with the pressure in the tower 4 and it is only important to regulate the temperature so as to prevent condensation of water. In this section, the ready polymerizable oils and remaining carbons and tars are removed by the oil quench. The second section of the tower is usually outfitted with more trays than the lower section, specifically from about four to five. Sieve trays or others can be used here. From this point, the substantially tarand carbon-free gas passes to an ordinary water quenching system within the tower 4.

The quench tower is usually outfitted with external quench oil coolers and circulation pumps although these can be omitted if a l-pass oil quench system is used. Efliuent oil from the lower section generally goes to the coker. Oil from the uppersection can go to the coker or to a fractionator column 3 where the lighter portion, high in aromatics, is removed. Bottoms from the separation go to the coker 3.

The oil 11 useful as quench is preferably in the boiling range of from 300 to 700 F., more preferably in the boiling range of from 450 to 650 F., and most preferably in the boiling range of from 500 to 600 F. Thus, atmospheric gas oil 7 from a crude unit tower may be used as a quench as may, more preferably, coker gas oil 10 from the coker 3. Enough oil as quench is contacted with the Wulff efliuent in the quench tower 4 to lower the temperature of the efliuents to a point preferably from to 20 F. and more preferably from to 15 F. above the condensation point of the steam in the effluent, which point is generally about 160 F. This prevents the steam in the effluent from condensing to form water and hence forming emulsions with carbon, readily polymerizable oils, and tars that are present in the eflluent. The quench oil has now removed a large percentage of the tars and other deleterious carbon compounds from the effluent. The mixture of used quench oil and tars is now separated 4 from the cleaned, cooled efliuent by gravity and is thereafter recycled 5 to the coker 3. The temperature of the quenched efiluent gases is now approximately from about 250 to F. Said efiiuent is now preferably quenched further 4 by a conventional water spray quenching apparatus which reduces the temperature of the efiluent gases to the desired level for purification 6'. Other liquids may be used as quench in this step, such as a hydrocarbon fraction, but water is more economical. Substantially no oil-water emulsions form.

Although the above process for quenching is preferred, a one step oil quench may be used with less attendant fouling than in the traditional water quench.

The quenched gas is now sent 6 through a purification process, which can be similar to that described in FIG. 5 of Wulfi Process Acetylene, Modern Chemical Processes, cited above. Although separation by solvent extraction, wherein the solvent may be dimethylformamide (DMF) for instance, is preferable, separation by means of an electrostatic separator is even more preferred. See for example copending application 545,452 filed Apr. 26, 1966, now Pat. No. 3,395,193.

The feed 7 to the coker 3 is preferably a hydrocarbon boiling in the range of greater than 600 R, such as atmospheric gas oil, which is preferably first sent to a fractionator 3 where the hydrocarbon is fractionated to produce lower ends that are sent to the coker 3. The coker simultaneously produces coker naphtha 8 useful as at least a portion of the feed for the Wnltf furnace 2, and coke 9. And further, the fractionator portion of the coker apparatus produces a coker distillate also called coker gas oil 10 to be used as the quench oil and cycled to the oil-quenching tower 4 for that purpose.

The most preferred embodiment of this invention is pictorially represented in the drawing, where the coker not only produces coke 9, partially feeds the Wulfi furnace with coker naphtha 8, feeds the quencher with coker gas oil 10, but also serves as a receptacle for the quench oil-tar mixture 5 which, along with other hydrocarbons 7 specified above, are coked 3 to complete the continuous cycle. In this embodiment, not only are the yields of acetylene and ethylene very competitive with other processes, but also the quench oil-tar mixture is conveniently recycled to the coker where it may improve the quality of the coke, coker naphtha, and coker gas oil produced. Furthermore, the compressors and other downstream equipment are essentially free from deposits.

It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto.

What is claimed is:

1. A process for the production of coke and acetylene by pyrolysis of hydrocarbons comprising heavy naphthas boiling in the range of approximately 200-400" F. said process comprising in combination the steps of:

(a) pyrolyzing hydrocarbons in the presence of steam in a regenerative type furnace for a residence time of less than about 10 seconds to produce a gas stream containing unsaturated hydrocarbons,

(b) quenching to rapidly reduce the temperature of said efliuent gas stream by contacting said stream with a distributed hydrocarbon liquid quench oil stream,

(c) recovering a stream of said quench oil containing tars removed from said effluent stream from said furnace,

(d) feeding at least a portion of said quench oil-tar mixture to a coker,

(e) coking said quench oil-tar mixture, together with other hydrocarbons in said coker to produce a coker naphtha, a coker gas oil, and coke,

(f) feeding at least a portion of said coker gas oil to said quenching step to constitute at least a portion of said quench oil,

(g) recovering from said quench step unsaturated hydrocarbons remaining in the vapor phase after said quench step.

2. The process of claim 1 wherein the regenerative type furnace is a Wulif furnace.

3. The process of claim 1 wherein the coker is a delayed coker.

4. The process of claim 1 wherein the hydrocarbons pyrolyzed comprise straight-run naphthas having a boiling range of from about 100 to 400 F.

5. The process of claim 1 wherein the pyrolysis occurs in the presence of from about 6 to 10 moles of steam per mole of hydrocarbon.

6. A process for the production of coke and acetylene by pyrolysis of hydrocarbons comprising heavy naphthas boiling in the range of approximately ZOO-400 F. said process comprising in combination the steps of:

(a) pyrolyzing hydrocarbons boiling in the range of from about 100 to 400 F. in the presence of steam in the ratio, in moles, of from about 6 to 10 of steam to hydrocarbon in a Wulif furnace at a temperature of from about 1500 to 2500 F. and for a residence time of less than about 10 seconds to produce a gas stream containing unsaturated hydrocarbons,

(b) quenching to rapidly reduce the temperature of said efiluent gas stream to about 0 to 20 F. above the condensation point of the steam diluent present by contacting said stream with a distributive liquid quench oil stream comprising a hydrocarbon fraction boiling in the range of from about 300 to about 700 F.,

(c) recovering a stream of hydrocarbon quench oil containing tars removed from said eflluent stream from said furnace,

((1) further reducing the temperature of said effluent gas stream by contacting said stream with a distributive stream of water,

(e) feeding at least a portion of said quench oil-tar mixture to a delayed coker,

(f) coking said quench oil-tar mixture, together with other hydrocarbons in said delayed coker to produce a coker naphtha boiling in the range of from about 100 to 400 F., a coker gas oil boiling in the range of from about 300 to 700 F. and coke,

(g) feeding at least a portion of said coker naphtha thus produced to said Wulfi' furnace,

(h) feeding at least a portion of said coker gas oil to said quenching step to constitute at least a portion of said quench oil,

(i) recovering from said quench step unsaturated hydrocarbons remaining in the vapor phase after said quench step.

7. The process of claim 6 wherein the feed to said coker is a distributive stream of hydrocarbon boiling in the range greater than 600 F.

8. In the quenching of a high temperature hydrocarbon stream by direct contact thereof with a hydrocarbon quench oil in a quench zone wherein a dirty hydrocarbon quench oil and a cooled hydrocarbon stream are removed from the quench zone, a process for regenerating the dirty hydrocarbon quench oil comprising:

(a) introducing dirty quench oil into a coker combination fractionator;

(b) recovering a high boiling bottoms from the coker combination fractionator;

(c) introducing high boiling bottoms into a coking heater to effecting heating thereof to coking temperatures at coking pressures;

(d) introducing heated high boiling bottoms into a coke drum to effect coking thereof;

(e) recovering coke from the coke drum;

(f) introducing overhead from the coke drum into the coker combination fractionator;

(g) recovering a coker distillate fraction from the coker-combination fractionator; and

(h) recycling at least a portion of the fraction to the quench zone as regenerated quench oil.

9. The process as defined in claim 8 wherein the high boiling bottoms is heated in the coker heater under coking conditions.

10. The process as defined in claim 9 wherein the high temperature hydrocarbon stream is derived from the pyrolysis of a hydrocarbon in a pyrolysis zone and further comprising: recovering the various components from the cooled hydrocarbon stream, including the heavy residues of the pyrolysis efiluent; and introducing at least a portion of the heavy residues into the coker combination fractionator along with dirty quench oil.

References Cited UNITED STATES PATENTS 2,905,733 9/1959 Boston et al 260-683 2,908,625 10/1959 Mekler et al 260--'683 DELBERT E. GANTZ, Primary Examiner C. E. SPRESSER, In, Assistant Examiner US. Cl. X.R. 208-54 

